Electrochemical Pump for Hydrogen Purification: Investigating Kinetic and Transport Properties in the Electrode layer
Restricted (Penn State Only)
- Author:
- Arunagiri, Karthik
- Graduate Program:
- Chemical Engineering
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- August 16, 2024
- Committee Members:
- Ezra Clark, Major Field Member
Derek Hall, Outside Unit & Field Member
Bert Chandler, Co-Chair & Dissertation Advisor
Phillip Savage, Major Field Member
Christopher Arges, Co-Chair & Dissertation Advisor
Robert Rioux, Professor in Charge/Director of Graduate Studies - Keywords:
- Electrochemical hydrogen pump
Hydrogen purification and compression
Electrode Binder
Gas transport
Kinetics
Phosphonic acid ionomer
Anhydride formation
Binder Blend - Abstract:
- Electrochemical pumping technology for hydrogen purification and compression offers significant advantages in the transition to a carbon-free hydrogen-based economy. A critical issue with low-temperature Nafion™-based electrochemical hydrogen pumps (EHPs) is their reliance on water vapor for proton conduction, necessitating water vapor removal downstream. Additionally, the electrocatalyst is susceptible to poisoning by impurities in hydrogen gas mixture. High-temperature EHP technology addresses these challenges by conducting protons anhydrously and mitigating electrocatalyst poisoning through elevated operating temperatures. In high-temperature EHPs, the electrode architecture plays a vital role in determining the effectiveness of hydrogen separation. The central focus of this dissertation is to study the electrode architecture to find how the kinetics and gas transport in the electrode layer affect the polarization of the EHP. The research explores various aspects of catalyst layer and their influence on the electrode processes in EHPs. The ionomer binder, which is in close contact with the electrocatalyst, plays a crucial role in facilitating gas transport to and from the catalyst surface, as well as the reactions occurring at the catalyst surface, in addition to its role in ionic conductivity within the electrode. A significant gap exists in understanding the effects of high-temperature ionomer binders on kinetics and gas transport in electrochemical systems. This study begins by examining the impact of phosphonic acid binders and their blends with sulfonic acid binders (high-temperature ionomers) on ionic conductivity, gas transport, and kinetics in EHP electrodes. Through a comprehensive experimental and modeling approach, it is demonstrated that an electrode ionomer blend of PTFSPA with Aquivion®, used as a binder in high-temperature PEM EHPs, achieved a current density of 5.1 A cm⁻² at 0.4 V using pure hydrogen, marking the highest reported value in the literature. Subsequently, the study evaluates the EHP's effectiveness in separating hydrogen from dilute hydrogen-natural gas mixtures. The influence of hydrogen concentration on EHP polarization, kinetics, and gas transport resistances was analyzed. Surprisingly, it was discovered that kinetic resistance varied significantly with hydrogen concentration due to interfacial mass-transfer resistance at lower hydrogen levels. To mitigate this, back pressure was applied, resulting in enhanced performance of 1.4 A cm⁻² for a 10 vol% hydrogen gas mixture. Furthermore, the dissertation provides an in-depth analysis of electrode binders’ transport properties, such as permeability , solubility and diffusivity as well as catalyst ink stability, which impacts catalyst layer homogeneity. The study also delves into investigation of alternative alkyl acids such as ethyl and methyl phosphonic acids dopped HT-PEMs, aimed at reducing the acid leaching from membrane to the electrodes. Overall, this dissertation advances the field of electrochemically driven pumps for hydrogen separations, making a significant contribution to the broader goal of achieving global sustainability.